I have been doing a lot of research and reading on both and my vote is for the S&S coupled bike.

I am having my 1984 Trek 720 retro fitted with S&S couplers. From everything I have read, a S&S coupled bike rides just like a standard bike, no difference.

with an S&S bike you use all the same equipment as you would on a regular DF bike. A folder may require special parts and different sized tires, etc. Just something to keep in mind when traveling, so not be a problem in most places, but it could be.